Total knee implant

ABSTRACT

A knee prosthesis is provided for use in knee arthroplasty. In one exemplary embodiment, the present invention provides a tibial prosthesis having a tibial baseplate with a fixed medial bearing component and a mobile lateral bearing component. In one exemplary embodiment, the lateral bearing component is secured to the lateral portion of the tibial baseplate utilizing at least one prosthetic ligament. Additionally, in one exemplary embodiment, a stop is provided to limit anterior or posterior movement of the lateral bearing component relative to the tibial baseplate. For example, the stop may be defined by cooperating shoulders formed on the lateral bearing and the tibial baseplate.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit under Title 35, U.S.C. §119(e) ofU.S. Provisional Patent Application Ser. No. 61/147,492, entitled TOTALKNEE IMPLANT, filed on Jan. 27, 2009, the entire disclosure of which isexpressly incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to orthopedic prostheses and,particularly, to knee prostheses.

2. Description of the Related Art

In a natural knee joint, the meniscus is positioned between the distalend of the femur and the proximal end of the tibia to provide cushioningand support to the tibia and femur as they rotate relative to oneanother. Additionally, the medial side of the meniscus is morestationary than the lateral side of the meniscus, which is more flexibleand/or mobile. The mobility of the lateral meniscus increases theability of the lateral condyle of the femur to roll off of the tibialplateau during high flexion of the knee, i.e., it increases the abilityof the femur to rotate into a position in which the lateral condyle isnot entirely supported by the tibial plateau.

In a fixed bearing tibial prosthesis, external rotation of the femoralcomponent against the tibial component can be limited due to the fixednature of the prosthesis. Thus, the lateral condyle of the femur isprevented from rolling off the tibial plateau. In order to provide forarticulation of the knee joint that better replicates the naturalarticulation of the knee joint, a mobile bearing tibial prosthesis maybe used. In a mobile bearing tibial prosthesis, the entirety of thetibial bearing, including both the medial and lateral condyles, isrotatable relative to a tibial baseplate. Additionally, in some mobilebearing tibial prostheses, the tibial bearing is rotatable about a pointpositioned on the medial condyle of the tibial baseplate. This resultsin increased lateral rotation of the bearing component, which bettermimics natural knee joint articulation.

Additionally, during a total knee arthroplasty, it may be necessary toresect the cruciate ligaments of the knee joint. This may result, forexample, in decreased support and stability in the patient's knee joint.

SUMMARY

The present disclosure provides knee prostheses for use in kneearthroplasty. In one exemplary embodiment, the present inventionprovides a tibial prosthesis having a tibial baseplate with a fixedmedial bearing component and a mobile lateral bearing component. In oneexemplary embodiment, the lateral bearing component is secured to thelateral portion of the tibial baseplate utilizing at least oneprosthetic ligament. Additionally, in one exemplary embodiment, a stopis provided to limit anterior or posterior movement of the lateralbearing component relative to the tibial baseplate. For example, thestop may be defined by cooperating shoulders formed on the lateralbearing and the tibial baseplate.

By providing a fixed medial component and a mobile lateral component fora tibial prosthesis, an articulating surface of a medial condyle of afemoral component may be highly conforming with an articulating surfaceon the medial component of the tibial prosthesis, which acts to controlanterior and posterior movement of the joint. Additionally, the mobilelateral component of the tibial component allows for a lateral condyleon a femoral component to undergo additional rollback, which is normallyprevented in both fixed and mobile tibial prostheses, in order to moreaccurately replicate the natural articulation of the knee joint.

In one exemplary embodiment, the present invention also includes afemoral component. In one exemplary embodiment, the femoral componentincludes a crossbar extending between opposing medial and lateralcondyles. In this embodiment, a prosthetic ligament is wrapped aroundthe crossbar and secured to attachment points on the tibial baseplate.The prosthetic ligament acts to replicate the function of the patient'sresected anterior cruciate ligament (ACL) by restricting movement of thefemoral component relative to the tibial component. In other exemplaryembodiments, a plurality of prosthetic ligaments may be provided thatare configured for attachment to a plurality of attachment points on thetibial baseplate and femoral components. In this manner, by selectivelypositioning the prosthetic ligaments with respect to the femoralcomponent and tibial baseplate, the natural articulation of the kneejoint for an individual patient may be more accurately replicated.

In other exemplary embodiments, provisional prosthetic ligaments may beutilized to facilitate the trialing of the femoral component and thetibial component. For example, in one exemplary embodiment, theprovisional prosthetic ligaments are designed to fail if the ligamentsare subjected to a tension that exceeds a predetermined tension limit.In one exemplary embodiment, opposing portions of the provisionalprosthetic ligaments may be secured to one another by magnets. Once atension that exceeds the predetermined amount of tension is applied tothe ligaments, the magnetic force between the two magnets that holds theopposing portions of the ligaments together is overcome, causing theligaments to fail. This allows a surgeon to trial the prostheticcomponent and, if the ligaments fail, the surgeon is provided with avisual and tactile indication that the patient's knee joint is tootight. In other exemplary embodiments, the provisional prostheticligaments may be designed to break if a tension in excess of apredetermined tension limit is applied to the ligaments. In anotherexemplary embodiment, the provisional prosthetic ligaments may bedesigned to separate from one of the femoral component and tibialcomponent if a tension is applied to the ligaments that exceeds apredetermined amount of tension.

Additionally, by allowing for the use of prosthetic ligaments, theability of a surgeon to replicate the natural articulation of a kneejoint for a particular patient is increased. For example, when aplurality of attachment sites are provided on the tibial and/or femoralcomponents, the surgeon may individually select attachment sites basedon specific physical characteristics of an individual patient. As aresult, the surgeon may more accurately replicate the natural kneearticulation for an individual patient. Further, by providingprovisional prosthetic ligaments that allow for separation and/orfailure of the provisional prosthetic ligaments if a tension thatexceeds a predetermined tension is applied to the provisional prostheticligaments, the surgeon may also test the knee joint to determine whetherthe joint is too tight. The provisional prosthetic ligaments provide avisual and/or tactile feedback that immediately indicates whether thejoint is too tight.

In one form thereof, the present invention provides a prosthetic kneesystem including a femoral component having a lateral condyle and amedial condyle and a tibial component having a base plate, a medialbearing surface and a lateral bearing surface. The baseplate includes abone facing surface and an opposing support surface. The medial bearingcomponent includes a medial articulation surface and a medial attachmentsurface, with the medial attachment surface coupled with the supportsurface of the baseplate to fix the medial component to the baseplate,so that movement of said medial component relative to said baseplate issubstantially entirely prevented. The lateral bearing component includesa lateral articulation surface and a lateral attachment surface, withthe lateral attachment surface slidingly secured to the support surfaceof the baseplate. The lateral component is translatable relative to thebaseplate.

In one aspect, a T-shaped projection may be formed on either the lateralattachment surface of the lateral component or the support surface ofthe baseplate, with a T-shaped groove formed on the other surface, i.e.,the surface without the T-shaped projection. The T-shaped projection maybe sized and positioned to cooperate with said T-shaped groove to form asecurement mechanism when the lateral attachment surface of the lateralcomponent is slidingly secured to the support surface of the baseplate,with the securement mechanism allowing translation of the lateralcomponent in an anterior direction and a posterior direction.

In another aspect, the baseplate may include a first baseplate shoulderformed on the support surface, and the lateral component may include afirst lateral component shoulder formed on the lateral attachmentsurface. The first baseplate shoulder and the first lateral componentshoulder may cooperate to limit either anterior translation or posteriortranslation of the lateral component.

In yet another aspect, the prosthetic knee system may include a firstprosthetic ligament with an elongate body, a first end, and a secondend, with the first end and the second end attachable to the tibialcomponent. The femoral component may include a crossbar disposed betweenthe medial condyle and the lateral condyle, with the elongate body ofthe first prosthetic ligament wrapped around the crossbar to couple thefemoral component to the tibial component.

In another form thereof, the present invention provides a prostheticknee system includes a femoral component, a tibial component and a firstprosthetic ligament. The femoral component has a lateral condyle and amedial condyle, and defines at least one femoral attachment point. Thetibial component has a lateral articulating surface and a medialarticulating surface, and defines at least one tibial attachment point.The first prosthetic ligament having an elongate body, a first end, anda second end, with the first end attachable to the femoral attachmentpoint of the femoral component and the second end attachable to thetibial attachment point of the tibial component, so that the femoralcomponent is coupled with the tibial component when the first prostheticligament is attached to the femoral attachment point and the tibialattachment point.

In one aspect, a second prosthetic ligament, or a plurality ofprosthetic ligaments may be provided to extend between posterior and/oranterior attachment points on the tibial component and lateral and/ormedial attachment points on the femoral component. In another aspect,means for severing the prosthetic ligament may be provided, such as apair of cooperating magnets disposed a first end and a second end of theprosthetic ligament, a weakened portion along a portion of the elongatebody of the first prosthetic ligament, and/or a connection between theprosthetic ligament and the femoral component or the tibial component.

In yet another form thereof, the present invention provides a method ofintraoperatively defining tension between components of a prostheticknee system, the method including: providing a femoral component havinga lateral condyle and a medial condyle, the femoral component definingat least one femoral attachment point; providing a tibial componenthaving a lateral articulating surface and a medial articulating surface,the tibial component defining at least one tibial attachment point;attaching a first end of a prosthetic ligament to the femoral attachmentpoint of the femoral component; attaching a second end of the prostheticligament to the tibial attachment point of the tibial component; andselecting a tension of the prosthetic ligament.

In one aspect, a plurality of prosthetic ligaments may have first endsattached to respective femoral attachment points, and the plurality ofprosthetic ligaments may have second ends attached to respective tibialattachment points. In another aspect, a provisional prosthetic ligamentmay be attached to the femoral attachment point and tibial attachmentpoint before the prosthetic ligament is attached and a tension thereofis selected. A tension in the provisional prosthetic ligament may bemeasured.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention itself will be better understood by reference to the followingdescriptions of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a perspective view of a tibial component and femoral componentof a total knee arthroplasty system;

FIG. 2 is an elevational view of the total knee arthroplasty system ofFIG. 1;

FIG. 3 is a perspective view of the tibial component of the total kneearthroplasty system of FIG. 1;

FIG. 4 is a cross-sectional view of the total knee arthroplasty systemof FIG. 1, taken along line 4-4 of FIG. 1;

FIG. 5 is an elevational view of a tibial component according to anotherexemplary embodiment;

FIG. 6 is a cross-sectional view of the tibial component of FIG. 5 takenalong line 6-6 of FIG. 5;

FIG. 7 is a cross-sectional view of a total knee arthroplasty systemdepicting a femoral component at 90 degrees of flexion with respect tothe tibial component, wherein the cross-section is taken in amedial/lateral direction that is slightly posterior relative to thetotal knee arthroplasty system, and in which prosthetic ligamentsaccording to an exemplary embodiment are also depicted;

FIG. 8 is a cross-sectional, plan view of a femoral component accordingto another exemplary embodiment depicting a plurality of prostheticligaments connected thereto;

FIG. 9A is a plan view of tibial component according to anotherexemplary embodiment depicting a plurality of prosthetic ligamentsconnected to anterior and posterior sides thereof;

FIG. 9B is a plan view of tibial component according to anotherexemplary embodiment depicting a plurality of prosthetic ligamentsconnected to a posterior side thereof;

FIG. 10 is a cross-sectional view of a total knee arthroplasty systemaccording to an exemplary embodiment depicting the femoral component in90° of flexion with respect to the tibial component, wherein thecross-section is taken in a medial/lateral direction that is slightlyposterior relative to the total knee arthroplasty system, and in whichprosthetic ligaments according to another exemplary embodiment are alsodepicted;

FIG. 11 is a fragmentary cross-sectional view of the total kneearthroplasty system of FIG. 10 taken along line 11-11 of FIG. 10; and

FIG. 12 is a cross-sectional view of a total knee arthroplasty systemaccording to another exemplary embodiment depicting a femoral componentat 90 degrees of flexion with respect to the tibial component, whereinthe cross-section is taken in a medial/lateral direction that isslightly posterior relative to the total knee arthroplasty system, andin which provisional prosthetic ligaments according to an exemplaryembodiment are also depicted.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate preferred embodiments of the invention and suchexemplifications are not to be construed as limiting the scope of theinvention in any manner.

DETAILED DESCRIPTION

Referring to FIG. 1, total knee arthroplasty system 10 is shownincluding femoral component 12 and tibial component 14. Femoralcomponent 12 includes anterior flange 16 and opposing condyles 18, 20,that extend from anterior flange 16. As shown in FIG. 1, total kneearthroplasty system 10 is configured for use in a left knee and, assuch, condyle 18 is a lateral condyle and condyle 20 is a medialcondyle. However, the principles of the present disclosure are equallyapplicable to a right or left knee. Extending between opposing condyles18, 20 is crossbar 22. Crossbar 22 is secured to opposing condyles 18,20 by base 24 and is designed to receive prosthetic ligament 26therearound, as defined in detail below. Crossbar 22 may also beintegrally formed in base 24, for example.

Tibial component 14 includes stem or keel 28 connected to baseplate 30.Tibial component 14 is configured for securement to a resected proximaltibia, such that stem or keel 28 is received within the resectedproximal tibia and baseplate 30 sits atop the resected proximal tibia.Extending upward from baseplate 30 is projection 32 that extends in ananterior/posterior direction across tibial component 14 and definesopposing medial and lateral sides of tibial component 14. Projection 32includes attachment points 34, 36 for receipt of opposing ends ofprosthetic ligament 26. When prosthetic ligament 26 is wrapped aroundcrossbar 22 as shown in FIG. 4, affixing ligament 26 to projection 32via attachment points 34, 36 secures femoral component 12 to tibialcomponent 14. Attachment points 34, 36 may include an adhesive, such asbone cement, to affix ligament 26 to projection 32. However, asdescribed in detail below, various securement methods are available toprovide proper affixation of ligament 26 to tibial component 14, as wellas to impart a desired tension between femoral component 12 and tibialcomponent 14. For example, multiple prosthetic ligaments 26 may besecured to femoral component 12 to achieve a desired tension betweenfemoral component 12 and tibial component 14. The length of prostheticligament 26 may also be varied.

Lateral and medial bearing components 38, 40, respectively, arepositioned atop and secured to baseplate 30. Lateral and medialcomponents 38, 40 define articulating surfaces 42, 44, respectively,that cooperate with condyles 18, 20 of femoral component 12 during kneearticulation. In one exemplary embodiment, medial bearing component 40is fixedly secured to tibial baseplate 30, such as by a snap-fit, toform a fixed medial component. Thus, in this embodiment, medialcomponent 40, once secured to baseplate 30, is substantially preventedfrom moving relative to baseplate 30. In contrast, lateral bearingcomponent 38 is secured to baseplate 30 to form a mobile bearingcomponent. Thus, in this embodiment, lateral component 38 is moveablerelative to baseplate 30 to encourage normal articulation and relativerotation between femoral component 12 and tibial component 14.

Specifically, in a normal knee joint, the femur rotates about a pointthat is medially offset, i.e., a point that is on the medial side of theknee joint, as the knee joint transitions between flexion and extension.As a result, lateral condyle 18 of femoral component 12 travels asubstantially greater arcuate distance than medial condyle 20 of femoralcomponent 12 along a plane extending across the proximal end of theresected proximal tibia as the knee travels between various stages offlexion and extension. In the illustrated embodiment of FIGS. 1-3,lateral condyle 18 is substantially symmetrical to medial condyle 20 infemoral component 12, and lateral component 38 is substantiallysymmetrical to medial component 40 in tibial component 14. The largerdistance traveled by lateral condyle 18 is facilitated by fixing medialcomponent 40 and allowing lateral component 38 to move, as describedbelow. However, it is also within the scope of the present disclosurethat asymmetrical tibial and/or femoral components may be used, such asby using relatively larger articulating surfaces on the lateral portionsof the components.

As indicated above, medial component 40 of tibial component 14 is afixed bearing component. For example, in one exemplary embodiment,articulating surface 44 may be a highly conforming articulating surface,meaning surface 44 is highly congruent with a mating structure such asmedial condyle 20. As a highly conforming articular surface,articulating surface 44 has a concave shape that substantiallycorresponds to the convex shape of the articulating surface of medialcondyle 20 of femoral component 12. As a result, the anterior andposterior movement of medial condyle 20 is controlled, while allowingfor rotation of femoral component 12 atop articulating surface 44 ofmedial condyle 20. In this manner, the natural movement of an anatomicmedial condyle with respect to an anatomic tibia is replicated by medialcondyle 20 and medial component 40.

In contrast to medial component 40 of tibial component 14, lateralcomponent 38 of tibial component 14 is a mobile bearing component. Forexample, in one exemplary embodiment, lateral component 38 may beadvanced anteriorly as femoral component 12 transitions from extensioninto flexion and, correspondingly, lateral component 38 may be advancedposteriorly as femoral component 12 transitions from flexion intoextension. Articulating surface 42 may be a less conforming articulatingsurface as compared to articulating surface 44, meaning articulatingsurface 42 is somewhat less congruent with the mating lateral condyle18. As a less conforming articular surface, articulating surface 42 hasa concave shape that defines a larger radial profile than lateralcondyle 18 of femoral component 12. This reduced congruence allows someanterior and posterior movement of lateral condyle 18 within lateralcomponent 38, consistent with the natural movement of an anatomiclateral condyle with respect to an anatomic tibia. Although conformityis somewhat reduced, articulating surface 42 and lateral condyle 18still sufficiently conform to facilitate transmission of force fromlateral condyle 18 to lateral component 38, with the transmitted forcesufficient to drive the anterior and posterior motion of lateralcomponent 38. Alternatively, articulating surface 42 may be a highlyconforming surface similar to articulating surface 44.

In one exemplary embodiment, shown in FIGS. 1-3, an anterior stop isprovided to prevent lateral component 38 from subluxing anteriorally. Inthis embodiment, baseplate 30 includes a stepped portion that definesshoulder 46, while lateral component 38 includes a corresponding steppedportion that defines shoulder 48. As lateral component 38 is advancedanteriorally, shoulder 48 of lateral component 38 contacts shoulder 46of baseplate 30 to prevent additional anterior movement of lateralcomponent 38 relative to baseplate 30. Once in this position, additionalflexion of femoral component 12 may result in femoral roll-off, i.e.,additional movement of lateral condyle 18 in a posterior direction awayfrom lateral component 38 of tibial component 14. Advantageously, byallowing for femoral roll-off of lateral condyle 18, total kneeprosthesis system 10 more accurately replicates the natural articulationof a knee joint. To maintain the overall stability of knee arthroplastysystem 10 during femoral roll-off, lateral component 38 may include aconvex portion at a posterior end thereof which is adapted to cooperatewith a concave posterior end formed in lateral condyle 18 during deepflexion. One exemplary knee implant with such cooperating convex andconcave portions is described in a U.S. Patent Application entitledLATERAL CONDYLE POSTERIOR INFLECTION FOR TOTAL KNEE IMPLANT (AttorneyDocket ZIM0730), filed on even date herewith, the disclosure of which ishereby incorporated by reference herein in its entirety.

In order to secure lateral component 38 to baseplate 30, baseplate 30may, in one exemplary embodiment, include projection 50 having aT-shaped cross-section that is received within a corresponding groove 52formed in lateral component 38. Due to the interaction of projection 50with the portion of lateral component 38 defining groove 52, lateralcomponent 38 may move anteriorly and posteriorly in the direction ofdouble-headed arrow A of FIG. 3, but is prevented from substantialmovement in a medial or lateral direction. In other exemplaryembodiments, projection 50 and groove 52 may be arcuate to allow forlateral component 38 and correspondingly condyle 18 to move along anarcuate path that has an axis of rotation that is medially offset withinrespect to the knee joint to further replicate the natural, anatomicalarticulation of the knee joint.

Referring to FIGS. 5 and 6, another exemplary embodiment of tibialcomponent 14 is shown as tibial component 54. Tibial component 54 issubstantially similar to tibial component 14 and corresponding referencecharacters have been used to identify identical or substantiallyidentical parts therebetween. Referring to FIG. 5, lateral component 55of tibial component 54 includes internal groove 56, shown in dashedlines in FIG. 5, that allows for lateral component 55 of tibialcomponent 54 to be snap-fit or otherwise secured to projection 58 oftibial baseplate 60. In this embodiment, movement of lateral component55 relative to tibial baseplate 60 is constrained only by theinteraction of internal side walls 61 and end walls 63, shown in dashedlines in FIG. 5, that define groove 52 with projection 58. For example,medial/lateral movement of lateral component 55 is substantiallyprevented by the interaction of sidewalls 61, shown in FIG. 6, withprojection 58. However, because projection 58 has a length that is lessthan the length of groove 52, lateral component 55 may move in ananterior/posterior direction until one of end walls 63 that definegroove 52 contact a corresponding end of projection 58. As a result ofthe increased length of groove 52 relative to projection 58, lateralcomponent 55 of tibial component 54 may be configured to be advancedsubstantially further in an anterior direction than lateral component 38of tibial component 14.

Additionally, due to the ability to configure lateral component 55 tomove further in an anterior direction than lateral component 38, ahighly conforming articulating surface may be formed on lateralcomponent 55. In this embodiment, as condyle 18 of femoral component 12moves in a posterior direction as the knee joint transitions fromextension to flexion, lateral component 55 would move in a posteriordirection with condyle 18. Similarly, as condyle 18 of femoral component12 moves in an anterior direction as the knee joint transitions fromflexion to extension, lateral component 55 would move in an anteriordirection with condyle 18. By having lateral component 55 of tibialcomponent 54 move with condyle 18 of femoral component 12, condyle 18may advance further in a posterior direction than can be achieved withknown femoral components.

In yet another exemplary embodiment (not shown), a lateral componentsimilar to lateral components 42, 55 may not have any restriction onmovement in the anterior or posterior directions. Thus, the lateralcomponent may be adapted to slide in a linear or arcuate path withoutany shoulders or end walls preventing the lateral component from furthermotion along the path.

As discussed in detail above, prosthetic ligament 26, shown in FIGS. 1and 4, may be secured to femoral component 12 and tibial component 14.By utilizing prosthetic ligament 26, movement of femoral component 12and tibial component 14 relative to one another is restricted. Thespecific restriction in the movement of femoral component 12 and tibialcomponent 14 relative to one another that is created by prostheticligament 26 may be designed to replicate the restrictions imposed onmovement of a natural knee joint by the cruciate ligaments. However, asshown in FIG. 2, knee arthroplasty system 10 may also be used withoutprosthetic ligament 26.

In still another alternative, only one of the two cruciate ligaments ina natural knee is replicated using prosthetic ligament 26. For example,a partial or total knee arthroplasty may utilize fixed medial component40 and/or mobile lateral component 38, while still retaining one or bothof the natural cruciate ligaments. In one exemplary embodiment shown inFIG. 9B, tibial component 14 may be designed for surgeries in which boththe posterior cruciate ligament (PCL) and the anterior cruciate ligament(ACL) are resected, but only the PCL is replaced with one or moreprosthetic ligaments 26. In this “cruciate retaining” design, lateralcomponent 40 and medial component 38 may be joined by bridge 39.Alternatively, a partial knee arthroplasty may be performed in whichonly a single side of the natural tibial plateau is replaced, so thateither medial component 40 or lateral component 38 may be used toreplace a resected articular surface on the medial or lateral side ofthe tibia, respectively.

In another exemplary embodiment, shown in FIG. 7, a pair of prostheticligaments 62 is shown. Referring to FIG. 7, each of prosthetic ligaments62 includes opposing spherical heads 66 and elongate body 68 extendingbetween opposing heads 66. In an exemplary embodiment, spherical heads66 are resiliently deformable and are sized to be received withincorresponding spherical grooves 70 provided at attachment points 72, 74that may formed on tibial component 14 and femoral component 12,respectively. The spherical shape of heads 66 and grooves 70 allow heads66 to articulate with grooves 70 as femoral component 12 and tibialcomponent 14 move relative to one another. By securing prostheticligaments 62 to femoral component 12 and tibial component 14, as shownin FIG. 7, the function of the anterior and posterior cruciate ligamentsmay be replicated by prosthetic ligaments 62. However, heads 66 may berigid or non-resilient, and need not articulate with attachment points72, 74. For example, heads 66 may be formed of a solid material, and/ormay be fixedly or permanently attached to attachment points 72, 74. Forexample, in some embodiments, prosthetic ligaments 62 may besufficiently flexible to obviate the benefits of spherical heads 66 andspherical grooves 70.

As shown in FIG. 7, attachment points 72 of tibial component 14 arespaced apart from one another in both an anterior/posterior dimensionand a medial/lateral dimension. Thus, in one exemplary embodiment, theanterior most attachment point 72 is positioned on the lateral side oftibial component 14, while the posterior most attachment point 72 ispositioned on the medial side of tibial component 14. Referring toattachment points 74 on femoral component 12, attachment points 74 areformed in opposing lateral and medial condyles 18, 20.

In one exemplary embodiment, ligaments 62 are formed as solid, flexibleligaments. In one exemplary embodiment, a plurality of ligaments 62 eachhaving a different stiffness is provided. By providing a plurality ofligaments 62 each having a different stiffness, a surgeon may select anappropriate stiffness of ligaments 62 to create a condition in whichtheir crossing interactions drive axial rotation of a femoral componentupon a tibial component during knee articulation. Moreover, ligaments 62can be selected based on a variety of ligament material properties toprovide optimal joint kinematics and soft tissue balance, as discussedin detail below.

In another exemplary embodiment, a locking mechanism (not shown) may beattached to femoral component 12 and/or tibial component 14 to lockspherical heads 66 of prosthetic ligaments 62 in position withinspherical grooves 70. Additionally, while described as having sphericalhead 66 and elongate body 68, prosthetic ligaments 62 may be connectedto femoral component 12 and tibial component 14 in any suitable manner.

Additionally, in order to replicate the function of individual naturalcruciate ligaments, a plurality of prosthetic ligaments 62 may be used.This provides the surgeon with an increased ability to reconstitute thefunction of the natural cruciate ligaments, such as by adjusting theflexion/extension balance of the knee joint and/or theanterior/posterior contact point of femoral component 12 on tibialcomponent 14. By using multiple ligaments, the natural structure andfunction of the natural anterior cruciate ligament (ACL) and/orposterior cruciate ligament (PCL) is more closely approximated, withdifferent fibers potentially supporting loads that vary throughout therange of motion.

Referring to FIGS. 8 and 9A, a plurality of attachment points 72, 74 areshown on tibial component 14 and femoral component 12. In use, a surgeonmay attach one of spherical heads 66 of a first ligament 62 to one ofattachment points 74 on femoral component 12 and then attach theopposing spherical head 66 to one of attachment points 72 on tibialcomponent 14. Then, the surgeon may trial the knee joint, i.e., actuatethe patient's knee joint through flexion and extension. Based on thesurgeon's observations during the trialing, the surgeon may determinethat use of a different attachment point 72, 74 for at least one ofspherical heads 66 of one of ligaments 62 may provide a more natural,anatomical articulation of the knee joint for an individual patient orthat the use of an additional prosthetic ligament 62 may beadvantageous.

If the surgeon does determine that a different attachment point 72, 74would be beneficial for the patient, the surgeon may then remove one ofspherical heads 66 of one of prosthetic ligaments 62 from its attachmentpoint 72, 74 and position it within another attachment point 72, 74. Therange of motion testing may then be repeated to determine if a properflexion/extension balance of the knee joint and/or theanterior/posterior contact point of femoral component 12 on tibialcomponent 14 has been achieved. If the articulation of the knee joint isstill not satisfactory to the surgeon, one of spherical heads 66 may beremoved by attachment points 72, 74 and placed at another of attachmentpoints 72, 74. This process may be repeated as necessary until thesurgeon has found positions for ligaments 26 that most accuratelyreplicates the natural, anatomical articulation of the knee joint. Theillustrated embodiment of FIGS. 8 and 9A show attachment points 72, 74for prosthetic ligaments 62 arranged in a similar fashion to thearrangement of natural anatomic ligaments. However, the orientation ofattachment points can have different patterns or orientations within thescope of the present disclosure, such as an orientation that is areverse or mirror of the illustrated orientation.

In another exemplary embodiment (not shown), a prosthetic ligament maybe provided that includes a central body portion with a plurality ofnecks extending from the central body portion, such as in a “Y”configuration where two necks extend from the central body portion or a“pitchfork” configuration where three necks extend from the central bodyportion. In addition, each of the necks may terminate at a sphericalhead 66, which may be secured to one of attachment points 72, 74 in asubstantially similar manner as described in detail above with respectto prosthetic ligaments 62. Additionally, in this embodiment, theprosthetic ligament may be attached at a plurality of attachment points72, 74 on each of and/or one of femoral component 12 and tibialcomponent 14. In this manner, additional variability may be introducedinto total knee prosthesis system 10 to allow for a more preciseadjustment of the articulation of the knee joint, as discussed below.

Referring to FIGS. 10 and 11, another exemplary embodiment of prostheticligaments 62 are shown as prosthetic ligaments 76. Prosthetic ligaments76 may be substantially permanently secured to dovetail inserts 78, 80.Dovetail inserts 78, 80 are configured to be received in correspondingdovetail grooves 82, 84, formed in tibial component 14 and femoralcomponent 12, respectively. In this manner, prosthetic ligaments 76 maybe preattached and readily positioned within or removed from femoralprosthesis system 10. In another exemplary embodiment, prostheticligaments 76 are not substantially permanently attached, but are readilyremovable from dovetail inserts 78, 80. In this embodiment, prostheticligaments 76 may be removed from and/or added to dovetail inserts 78, 80to provide a desired configuration for an individual patient's kneejoint. For example, a plurality of prosthetic ligaments 76 may beprovided in which each prosthetic ligament 76 has a differentcharacteristic or a combination of different characteristics. Forexample, each prosthetic ligament 76 may have a different stiffnessand/or different length than other prosthetic ligaments 76, or may bemade of a different material. In this manner, a surgeon may select aprosthetic ligament 76 that has the characteristics that allows for themost accurate replication of the natural, anatomical articulation of thepatient's knee joint.

While described in detail above as having a specific design, includingspherical heads and elongate bodies, prosthetic ligaments 26, 62, 76,may take a number of different forms. For example, instead of beingformed as a solid, flexible prosthetic ligament and providing a varietyof different thicknesses, prosthetic ligaments 26, 62, 76 may be wovenor rope-like in order to determine the passive envelope of soft tissuein the knee joint and to provide anterior/posterior translation limitsfor the femur upon the tibia.

Additionally, variable properties of prosthetic ligaments 26, 62, 76 maybe manipulated to allow the surgeon to optimize the kinematics and feelof the knee prosthesis, e.g., by providing tight ligaments for jointstability and loose ligaments for joint laxity. Examples of suchproperties include: the number of prosthetic ligament strands in amulti-strand design; the size or diameter of prosthetic ligamentstrands; the material from which the prosthetic ligament is made; thelength and/or tension of the prosthetic ligament within the kneeprosthesis; the orientation of fibers relative to one another, i.e. a“Y” oriented fiber as discussed above; and the location of attachment ofprosthetic ligament strands, also discussed above. The surgeon may varythese or other characteristics of prosthetic ligaments 26, 62, 76 for anindividual patient to better match the needs of the patient, and tocompensate for differently shaped femurs, different genders, differentexpected level of athletic abilities and activities, and/or differentages between patients.

Moreover, varying the properties of prosthetic ligaments 26, 62, 76provides an opportunity for the surgeon to balance the soft tissues ofthe knee, and to reproduce as closely as possible the function of thenatural cruciate ligaments. Further, several ligament properties can bevaried intra-operatively. For example, a surgeon may vary the lengths ofprosthetic ligaments 26, 62, 76 at the time of implantation, such as bytrimming a portion of the ligament to create the desired length andtension. A cut-to-length prosthetic ligament 26, 62, 76 may bepre-attached to either femoral component 12 or tibial component 14, sothat only one end of prosthetic ligament needs to be cut to length uponattachment to the other component. Similarly, in the multi-strand designshown in FIGS. 8 and 9A, strands having different properties can beadded, removed or substituted until the desired soft tissue balance andjoint kinematics are achieved.

Referring to FIG. 12, provisional prosthetic ligaments 86 are shown.Provisional prosthetic ligaments 86, 88 are substantially similar toprosthetic ligaments 62, and corresponding reference numerals have beenused to identify identical or substantially identical partstherebetween. As shown in FIG. 12, elongate bodies 68 of provisionalprosthetic ligaments 86 are divided into two individual sectionsconnected to one another by opposing attractive magnets 90, 92. In thisembodiment, the force required to separate magnets 90, 92 is known andis selected to be at a level above which the total knee arthroplastysystem 10 would be considered to be too tight during articulation. Thus,if system 10 is too tight, then, during range of motion testing, magnets90, 92 will separate from one another and provide immediate visual andtactile feedback to a surgeon indicating that the knee joint is tootight.

As an alternative to magnets 90, 92, provisional prosthetic ligaments 86may be designed such that elongate bodies 68 fail upon the applicationof a force in excess of a predetermined limit, either along the extentof elongate body 68 or at one end thereof. For example, elongate body 68may have a weakened portion of known failure strength, or the entiretyof elongate body 68 may have a known failure strength. Alternatively,the moorings between elongate body 68 and femoral component 12 and/ortibial component 14 (such as at spherical heads 66) may have a weakenedportion or known failure strength. Thus, if the joint is too tight,elongate bodies 68 of provisional prosthetic ligaments 86 will fail byeither breaking or releasing from their moorings on femoral component 12and/or tibial component 14, which will also provide immediate visual andtactile feedback to the surgeon indicating that the joint is too tight.Prosthetic ligaments 86 utilizing magnets or breakage allow an indirectmeasurement of tension therein, in that an unbroken prosthetic ligamentsignifies that tension is below the breakage threshold and a brokenprosthetic ligament signifies a tension above the breakage threshold.

A further alternative for provisional prosthetic ligaments 68 mayinclude coupling instrumentation to one or more of ligaments 68 toprovide data feedback on the level of strain and/or force beingexperienced by ligaments 68. For example, a strain gauge may be coupledto a provisional prosthetic ligament 68 of known elasticity, so that agiven increase in length of the strain gauge is known to correspond to agiven force. Prosthetic ligaments 86 utilizing data feedback allowdirect measurement of tension therein, so that the tension at any givenflexion may be measured.

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

1. A prosthetic knee system, comprising: a femoral component having alateral condyle and a medial condyle; and a tibial component comprising:a baseplate having a bone facing surface and an opposing supportsurface; a medial bearing component having a medial articulation surfaceand a medial attachment surface, said medial attachment surface coupledwith said support surface of said baseplate to fix said medial componentto said baseplate, whereby movement of said medial component relative tosaid baseplate is substantially entirely prevented; and a lateralbearing component having a lateral articulation surface and a lateralattachment surface, said lateral attachment surface slidingly secured tosaid support surface of said baseplate, wherein said lateral componentis translatable relative to said baseplate.
 2. The prosthetic kneesystem of claim 1, further comprising: a T-shaped projection formed onone of said lateral attachment surface of said lateral component andsaid support surface of said baseplate, a T-shaped groove formed on theother of said lateral attachment surface of said lateral component andsaid support surface of said baseplate, T-shaped projection sized andpositioned to cooperate with said T-shaped groove to form a securementmechanism when said lateral attachment surface of said lateral componentis slidingly secured to said support surface of said baseplate, saidsecurement mechanism allowing translation of said lateral component inan anterior direction and a posterior direction.
 3. The prosthetic kneesystem of claim 1, wherein lateral component is translatable relative tosaid baseplate along a linear path.
 4. The prosthetic knee system ofclaim 1, wherein lateral component is translatable relative to saidbaseplate along an arcuate path.
 5. The prosthetic knee system of claim1, wherein said baseplate comprises a first baseplate shoulder formed onsaid support surface, and said lateral component comprises a firstlateral component shoulder formed on said lateral attachment surface,said first baseplate shoulder and said first lateral component shouldercooperating to limit one of anterior translation and posteriortranslation of said lateral component.
 6. The prosthetic knee system ofclaim 5, wherein said baseplate comprises a second baseplate shoulderformed on said support surface, and said lateral component comprises asecond lateral component shoulder formed on said lateral attachmentsurface, said second baseplate shoulder and said second lateralcomponent shoulder cooperating to limit the other of anteriortranslation and posterior translation of said lateral component.
 7. Theprosthetic knee system of claim 1, wherein said lateral condyle of saidfemoral component cooperates with said lateral articulation surface tourge said lateral component to translate relative to said baseplate. 8.The prosthetic knee system of claim 1, further comprising a firstprosthetic ligament having an elongate body, a first end, and a secondend, said first end and said second end attachable to said tibialcomponent, said femoral component comprising a crossbar disposed betweensaid medial condyle and said lateral condyle, said elongate body of saidfirst prosthetic ligament wrapped around said crossbar to couple saidfemoral component to said tibial component.
 9. A tibial prosthesiscomprising: a baseplate having a bone facing surface and an opposingsupport surface; a medial bearing component configured to be fixedlysecured to the baseplate, whereby movement of the medial bearingcomponent relative to the baseplate is substantially entirely preventedsuch that the medial bearing component is a fixed bearing component; anda lateral bearing component discrete from the medial bearing componentand configured to be slidingly secured to the baseplate, whereby thelateral bearing component is moveable relative to the baseplate suchthat the lateral bearing component is a mobile bearing component. 10.The tibial prosthesis of claim 9, wherein the baseplate includes aposterior end, an anterior end opposite the posterior end, a medialside, and a lateral side opposite the medial side, and wherein thelateral bearing component is movable in an anterior/posterior directionrelative to the baseplate.
 11. The tibial prosthesis of claim 10,wherein the baseplate and the lateral bearing component are configuredto prevent substantial movement of the lateral bearing component in amedial/lateral direction.
 12. The tibial prosthesis of claim 9, whereinthe lateral bearing component comprises a feature sized and positionedto cooperate with a corresponding feature on the baseplate to form asecurement mechanism when the lateral bearing component is slidinglysecured to the baseplate.
 13. The tibial prosthesis of claim 12, whereinthe feature on the lateral bearing component is a T-shaped groove formedon a lateral attachment surface of the lateral bearing component, andthe corresponding feature on the baseplate is a T-shaped projectionformed on the support surface of the baseplate.
 14. A prosthetic kneesystem comprising: a femoral component having a lateral condyle and amedial condyle; and a tibial component comprising: a baseplate having abone facing surface and an opposing support surface; a medial bearingcomponent configured to be fixedly secured to the baseplate, wherebymovement of the medial bearing component relative to the baseplate issubstantially entirely prevented such that the medial bearing componentis a fixed bearing component; and a lateral bearing component discretefrom the medial bearing component and configured to be slidingly securedto the baseplate, whereby the lateral bearing component is moveablerelative to the baseplate such that the lateral bearing component is amobile bearing component; and a prosthetic ligament coupled to thetibial component and configured to secure the femoral component to thetibial component.
 15. The prosthetic knee system of claim 14, whereinthe prosthetic ligament has an elongate body, a first end, and a secondend, the first end and the second end attachable to the tibialcomponent, and the femoral component comprises a crossbar disposedbetween the medial condyle and the lateral condyle, the elongate body ofthe prosthetic ligament wrapped around the crossbar to secure thefemoral component to the tibial component.
 16. The tibial prosthesis ofclaim 14, wherein the baseplate includes a posterior end, an anteriorend opposite the posterior end, a medial side, and a lateral sideopposite the medial side, and wherein the lateral bearing component ismovable in an anterior/posterior direction relative to the baseplate.17. The tibial prosthesis of claim 16, wherein the baseplate and thelateral bearing component are configured to prevent substantial movementof the lateral bearing component in a medial/lateral direction.